1. Field of the Invention
The present invention is concerned with a synchronizing mechanism for office chairs as they are known from DE 198 10 768 A1 or DE 101 25 994 A1, which accords to U.S. patent application Ser. No. 10/147,033 and is based on an older application of the applicant""s.
2. Background Art
The term xe2x80x9csynchronizing mechanismxe2x80x9d means structural components in the substructure of an office chair, which provide for kinematics that involve a certain coupled motion of the seat relative to the backrest. Placed on a chair column is a base carrier on which, on the one hand, is mounted a seat carrier, which is pivotable about a transverse axis and articulated to the base carrier and, on the other hand, a backrest carrier, which is also pivotable about a transverse axis and articulated to the base carrier. Mounted on the seat carrier is the seat of the office chair, which is as a rule provided with an upholstered seat surface. Conventionally, the backrest carrier extends backwards from the actual synchronizing mechanism, supporting the backrest of the office chair on an upward extension arm.
The seat carrier and backrest carrier are coupled in an articulated fashion such that pivoting the backrest backwardsxe2x80x94which is caused for instance when a person sitting on the chair leans back against the backrestxe2x80x94induces a lowering motion of the rear edge of the seat. This correlated seat-backrest motion brings with it a considerable comfort value and is desirable for orthopedic reasons.
To permit a backward downward pivoting of the backrest and seat in the case of a pure pivot-coupling of the backrest carrier to the base carrier and seat carrier, a degree of freedom must be introduced into the mechanism that permits the seat carrier to be shifted backwards while simultaneously allowing it to pivot about its front end. To this extent, the printed specifications of the prior art mentioned at the beginning reveal a turning-and-sliding joint between the base carrier and front end of the seat carrier. Depending on whether and how pronounced an elevating motion of the front edge of the seat is desired during the sliding-pivoting motion, the elongated-hole-type sliding guide for the seat carrier is either more steep, as in DE 198 10 768, or more flat, as in DE 101 25 994 A1 which accords to U.S. application Ser. No. 10/147,033.
An additional fundamental fact with synchronizing mechanisms lies in their spring action that counters the pivoting towards the rear. A multitude of spring designs is known from the prior art to achieve this. In the synchronizing mechanism according to DE 198 10 768 A1, the combination of a gas and a helical compression spring is provided, which extends as a relatively high unit under the seat carrier. One point of action of this spring arrangement is the front bearing end of the seat carrier; with its rear-facing end the spring arrangement is supported in a counter bearing in front of the cone receptacle for the seat carrier.
The spring arrangement provided in the design according to DE 101 25 994 A1, corresponding to U.S. application Ser. No. 10/147,033, is based on two leg springs that are housed in the base carrier. One leg of the spring is housed in an adjusting arrangement in the base carrier, whereas the second leg projects upward toward the seat carrier, which is supported on this leg by means of a corresponding counter bearing, and its backward pivoting direction is countered in this manner.
Both spring arrangements according to the prior art take up a considerable amount of the available component space in the base carrier, so that relatively narrow margins are set for its free design. Specifically, when known synchronizing mechanisms of this type are used, the base carriers, for optical-esthetic reasons, will have relatively voluminous casings to hide the spring arrangement and associated adjusting elements as best as possible.
Regarding the problems concerning the adjustability of the pretension of the spring arrangement, reference is made to DE 100 08 453 C2, which reveals a spring package with spring units that can be selectively switched on and off to vary the spring pretension and, hence, the counterforce against the pivoting. The spring arrangement itself, however, in this case is disposed between the base carrier and a one-piece combined seat and backrest carrier, which can be swiveled back as a whole. This does not represent a synchronizing mechanism per se.
The invention has as its object to improve a synchronizing mechanism for office chairs in such a way that the spring arrangements, while having a simple design, can be disposed particularly compact and specifically in closer spatial proximity underneath the seat carrier, so that the region of the base carrier essentially remains free while attaining the greatest degree of freedom for design options.
This object is met by the invention, according to which
the spring arrangement incorporates at least one helical compression spring disposed essentially parallel to the sliding direction of the seat carrier flat underneath it, wherein
for each helical compression spring, a counter-bearing extension arm is provided, the front end of which is articulated to the base carrier and the rear-facing end of which, freely projecting, forms a counter bearing for the rear support of the helical compression spring, and
the at least one helical compression spring is supported in each case with its front end on a counter bearing formed on the seat carrier.
Based on the described design, the entire spring arrangement is connected practically only via its front end to the remaining kinematics of the synchronizing mechanism. Proceeding from the front end of the counter-bearing extension arm, which is disposed at the height of the turning-and-sliding joint between the seat carrier and base carrier, the spring arrangement extends practically horizontally backwards along the seat carrier. Due to its flat design it has a very low construction height. Additionally, since no connecting elements are present at all that project downward toward the backrest carrier or base carrier, this region can be taken up by other construction and design elements of the chair as desired.
The basic design of the spring arrangement based on the counter-bearing extension arm also permits preferred improvements wherein the pretension of the spring arrangement can be adjusted in a simple manner. The counter-bearing extension arm must merely be supported sliding in the longitudinal direction of the seat. A sliding in the longitudinal direction changes the position of the counter bearing for the rear support of the helical compression spring, which, as a result, is compressed either to a greater or lesser degree with a corresponding change in the pretension. The sliding of the counter-bearing extension arm is preferably implemented by means of an adjusting shaft with eccentric cams.
According to an additional preferred embodiment, the spring arrangement is provided in the form of a spring package of multiple helical compression springs, the combined pretension of which is variable through a varying gradation in narrow steps of the individual eccentric cams of the adjusting shaft. This has the advantage on the one hand that a good balancing of the counterforce can be attained in the synchronizing mechanism with a wide absolute range of variations. As opposed to the design according to the above-mentioned DE 100 08 453 C2, the possibility to switch individual springs on or off is completely dispensed with.
Additional preferred embodiments of the invention provide for the design of the counter-bearing extension arms as rods on which the helical compression springs are placed. The helical compression springs may be supported via a bearing strip on the counter bearing of the seat carrier, said bearing strip being pivotably slide-mounted inside a bearing cutout of the counter bearing. The support of the helical compression spring towards the seat carrier is improved in this manner since a certain swivel angle must be offset in the support for the helical compression spring due to the rearward downward movement of the seat carrier plate when the synchronizing mechanism is actuated.
Additional preferred embodiments relate to the design of the bearing head of the given counter-bearing extension arm in the form of a frame, which is used on one hand to support the counter-bearing extension arm on the base carrier, and on the other hand as a working surface for the eccentric cams of the adjusting shaft.
According to additional preferred embodiments, a supplemental counter bearing that is adjustable in the longitudinal seat direction is provided on at least one counter-bearing extension arm at its rear-facing end. It allows for the helical compression spring on this counter-bearing extension arm to be varied in its initial pretension so that, together with the adjustability of the counter-bearing extension arm itself, at least two different counterforce ranges are provided to adjust the synchronizing mechanism to light-weight or heavyweight persons. Within these ranges, a fine-tuning can then be performed via the actual adjustment of the counter-bearing extension arms.
Lastly, in an additional variant of the invention, the at least one counter-bearing extension arm is executed as an adjusting shaft, which, on the one hand is rotation-drivable by an actuator on the base carrier, and on the other hand is provided with its rear-facing end with an adjustable counter-bearing end stop. The same is adjustable spindle-like by a rotation of the shaft in the direction of the spring force of the helical compression spring, so that the pretension of the helical compression springs is adjustable in a simple manner across wide ranges simply by operating the actuator.
The actuator is preferably formed by a manually operated actuation shaft located in the front region of the base carrier and coupled via a deflection gear to the front end of the adjusting shafts. Adjusting the spring pretension can thus be accomplished conveniently by means of a turning knob at the end of the actuating shaft laterally projecting from the chair.
A structurally simple support of the adjusting shafts is obtained in such a way that they are rotatably supported with their front end in a bearing yoke disposed on a deflection gear shaft. To attain a compact method of construction the deflection gear is formed as a bevel gear in each case between an adjusting shaft and a gear shaft driven by the actuating shaft. Additional characteristics, details and advantages of the invention will become apparent from the following description, in which one embodiment of the subject of the invention will be explained in more detail based on the drawings.